Experienced this issue multiple times and these following steps seem to remedy the situation every single time.
* Make sure to have both your tv and PS4 (PRO) powered off.
* Make sure to have the HDMI-cable not connected to your PS4
* Power-on your tv and set it to the corresponding HDMI-channel
* Press and hold your PS4 (PRO) power button and wait for the second beep to occur (this will enable safe mode)
* After you hear the second beep, connect your HDMI cable to your console
* Safe Mode will then come online, make sure to check for new updates (i found out that this issue tends to come up everytime Sony pushes a new software update).
* This update should remedy the situation, the console will most likely boot up a few times afterwards. Don’t cut the power on this boot sequence.
* Afterwards the problem should be resolved. If not, go back into safe mode and check your resolution. Put this on 720p just to be sure -> you can always change it back to your preferred resolution when the console is fixed via Options -> Sound & Screen.
Hope this helps someone out there. Cheers!